Electrical testing set.



' H. SKINNEH.

Y ELECTRICAL TESTING SET.

APPLICATION FILED IAAYZT. YI9I6.

Paten-1I Aug. 14,1917.

4 'mains-sum1.

" IMEI 1 l B. H. SKINNER.

ELECTRICAL TESTING SET.

.APPLICATION FILED MMU. I9I6.

1,2369491 Patented Aug. 14, 1917. I

4 SHEETSSHEET 2,

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III-I lllll II IIT'- IIIIII: I. IIIIIIII 1 im 'i' "II 'B'. H. SKINNER. ELEcTRlcAL TEsTmG ,s E.

' APPLlCATlON FILED MAY 27| 1916. l Patented Aug. 14, 1917.

4 sHEETs-sHEEr 3.

B. H. SKINNEH. ELECTRICAL TESTING SET. APPLICATION FILED IIIQY 21, IsIe.

Patented Aug. 14, 1917.

4 SHEETS-SHEET 4.

Imm or" Bezymnfz H Skinner V STATES PATENT BENJAMIN H. SKINNER, OF"BERWYN, ILLINOIS, ASSIGNOB. TO WESTERN ELECTRIC COMPANY, OF NEW YORK, Y., A CRPORATION 0i? NEW YGRK.

maaier Specification of Letters Patent.

ELECTRICAL TESTING SET.

Patented dug?. lid, 191W.

Application filed May 27, 1916. Serial itc-100,222...

NER, a citizen of the United States, residing at Berwyn, in the county of Cook and Stateof'Illinois, have invented certain new and useful Improvements in Electrical Testing Sets, of which the following is a full, clear, concise7 and exact description.

This invention relates to an improved electrical testing set particularly adapted forl use in telephone central exchanges.

In telephone exchanges, various tests must periodically be made on the relays, resistance coils, resistance circuits and other ap` paratus and circuits to insure proper and eflicient operation of the telephone system under normal conditions. For example, the vario-us relays which control the signaling,- talking yand ringing circuits must be periodically tested and adjusted, if necessary, so that. they will properly respond. A relay must 'respond and operate eliiciently when an operating current at or above a certain value is sent through the energizing winding, and the relay must not operate or respond when the current sent therethrough is below a certain predetermined value. The relay, ailier being' operated, must hold and must not release-'up to a certain current reduction, and must release when a predetermined current minimum is reached.

The above tests are the ones ordinarily made in central exchanges. Heretoore, such more or less disorderlyand inefficient manner. The variousV resistanoes, signals, switches and other parts have been connect- A ed b v lengths of wires, andfconductors were run to ground and to battery. Vith this temporary and somewhat crude arrangement. contacts and connections can readily loosen or .become broken and the testing is laborious, tedious, time-consuming, and more or less uncertain.

The object of the invention is to provide means for greatly simplifying such testing and to make it more certain and reliable by so arranging and mounting the various resistance elements, switches, signals, keys,

etc., in a housing or box of small size, with the various parts permanehtly connected together, that it will be unnecessary tov run' special conductors toget the necessary connections for testing. An important feature of my invention is that ordinary switchboard cords can be utilized for connecting ground and battery, and the various relays to be tested, with the test set. Such cord connections are the only connections necessary with my test set. Such connections in the set include circuit building switches, variable resistances, indicating instruments and signals, circuit closing keys, plug rcceiving jacks, etc., and after connection with the test set of ground and battery, and the relay or other device to be tested, the desired circuits are set up and controlled and results observed on the instruments and signals.

Another object consists -in an improved test set in which a plurality of adjustable resistances are employed, on each oi. which a plurality of resistance tests may be simultaneously set up which may thereafter be successively connected into' the testing circuit for the purpose of making a plurality of tests. This arrangement will permit a resistance setting for a plurality of tests, any one of which may be made at will without in any way disturbing the resistance settings o n the same coils for any of the other tests.

The improved test set and its uses illustrated in the accompanying drawings in which- Figure lis a. plan view of a test set whiciL embodies the invention;

Fig. 2 is a side elevational view of the testing apparatus with the inclosure in section;`

Fig. 3 is an end view of the supporting plate and apparatus mounted thereon;

Fig. 4 isa circuit diagram illustrating the operation and utility of the device; and

F ig. 5 is`a theoretical diagram showing the circuit connections used for switching the various Vresistances into the test circuit.

The inclosure shown comprises a rectangular box 5 to which a cover is attached by separable hinges 7, a handle 8 and a lock 9 being provided. Detachably'mounted in the box at the topI thereof is a supporting plate or` base 10 for the testing apparatus and circuit. Describing iirst the apparatus, five switch levers, 11, 12, 13, legend 15 are mounted on the base .as shown. For the lever 11 contactsl, 17, 18, 19 and 2O are provided; for lever 12 contacts 21, 22, 23, 24 and 25 are provided; for switch lever 13 contacts 26, 27 and 28 are provided; for

lbe about 1,200 ohms.

switch lever 14 contacts 29, 30, and 31 are provided; and for switch lever 15 contacts 33 vand 34 are provided. In front of the switches is a row of terminal posts 35, 36, 37, 38, 39 and 40, and, in front of these posts, the thimbles of spring jacks 41, 42, 43, 44, 45 and 46 are mounted in the base 10. Each of the jacks 41, 42, 43 and 44 has a tip contact spring 47 and a sleeve contact spring 48, and the contacts 49 and 50 normally engage with the springs 47 and 48 respectively. Each of jacks 45 and 46 has a spring 51, springs 52 and the thimble 53 for receiving respectively' the tip, ring and sleeve of A switch-board plugs.

To the rear of the switches, supporting disks 54 and 55 are mounted, between which is supported the terminal cylinder built up of Contact disks 56 and insulating disks 57 arranged alternately, the Contact disks being connected with the various resistance coils 58 which are suspended from the bottom of the base 10. Supported on and bridging between the end disks 54 and and parallel with the terminal cylinder are the bars 59, 60, 6l and 62, on which contact brushes 63, 64, 65 and 66, respectively, are slidably mounted. The contact point or end 67 of each brush may be brought into engagement with any terminal disk 56 as the brush is slid on its bar. The base 10 also supports end disks 68 and 69 between which is suspended the resistance coil or winding 70. Brushes 71, 72, 73 and 7 4 are slidable on bars 7 5, 7 6, 77 and 78 which are supported on the end disks 68 and 69 parallel with the resistance winding so that, when a brush is shifted on its bar, its contact point 79. will be brought into contact with any turn of the resistance winding. As will be shown later, the resistance 58 and the resistance 70 are connected in series., The resistances 58 bridged across the terminal disks 56 are of desired values. For telephone exchange testing, these resistances could range from 1000 ohms to 10,000 ohms so thatthere would be from 1,000 to 50,000 ohms resist-- The resistance should In practice, the brushesfor the resistances 58 are set as close4 ance available.

as possible .to the resistances desired and then the corresponding brushes of the resist ance 70 are shrifted to getaccurately the actual resistances desired.

Secured to the base 10 below'the 4sight opening is a milli-arnmeter 81 whose needle 82 coperates with the scale 83. The ammeter has two coils 84 and 85 (Fig. 4). When the coil 84 is in circuit, the needle which is normally on a central zero indica tion AWill indicate in either direction on the 0-150 scale, while, when 'the coil 85-is in circuit, the needle will indicate on the 0-30 scale. y

In front of the ammeter is a row7 of keys 86, 87,88, 89, and 91, the key 91 determining which coil of the ammeter shall be included in circuit. Each of the keys 86 to 90 comprises two terminal springs 92 and 93, and a contact button 94 which when depressed electrically connects the sA rings. All the keys except key 89 are non-locilring. Key 89 is locking and for this purpose its button 94 may have a locking groove 94 for receiv.- ing the ends of springs 92 and 93 when the button is depressed.

Behind the keys 86 to 91 is a-row of signals 95, 96, 97, 98 and 99, the signals 97, 98 and 99 being electrical lamps, while the signals and 96 comprise targets controlled by electromagnets.

Describingv now the circuit connections within the test set, the springs 92 of keys 86 to 89, inclusive, are connected by conductors 100, 101, 102 and 103 with the brushes 63, 64, 65, and 66, respectively, associated with the resistance 58. The other springs 93 of these keys are connected by conductors 104, 105, 106 and 107 with the brushes 71, 72, 73 and 74 respectively associated with the resistance 70. The .common terminal of resist ance 70 is connected by conductor 108 with the switch arm 14, while the common terminal of resistance 58 is connected by conductor 109 with the terminal 110 of the ammeter 81. The coil 85 of the ammeter connects with the terminal 110 and by conductor 111 is connected with the contact 112 of the key 91. The other coil 84 of the ammeter connects with the terminal 110 and by conductor 113 is connected with the contact 114 of the key 91. .Normally the button of the key is up and the\key spring 115 is-inwith a switch-board jack, the plugs at the end of a connecting c ord can be inserted respectively into the switch-board spring` jack and into one of the spring jacks 45 and 46 of the test set. As shown, the tip springs 51 of the springT jacks45 and 46 and the binding post 38 are connected together and by conductor 117 are connected with switch arm 11. The ring springs 52 ofthe jacks and the terminal post 39 are connected together and by conductor 118 are connected With the switch arm 12. The sleeve contacts 53 of the jacks and the binding post 40,:1re connected togetherl and by conductor 119 are connected with the switch arm 13.

Battery and ground may be supplied to 'the test set by running battery and ground springof jack 44. Contact 26 nected by conductor conductor to the binding posts 36 and 37, respectively. However, the subscribers answering cords on the station switch-boards have their tip sides connected with ground and their sleevesides connected with battery. The spring ia'cks 41, 42, 43 and 44 are provided forreceiving cords in order that battery and ground connection may be supplied to the testing set without requiring running of special conductors. -Upon yplug 4connection of answering cords A with the spring jacks, the spring 447 will be connected with ground and the springs 48 with battery.

. The contact 16 for the switch arm 11 is connected by conductor 120' with one terminal of the signal 95 whose other terminal is connected by conductor 121 v'with 'the sleeve spring 48 of the spring jack' 44, the contact 49 of this spring jack beingfconnected with sleeve spring of jack 42, the contact 49 of this jack being connected with contact 49 of jack 41 and with the binding post 37. The contact 17 for switch arm 11 is connected by conductor 122 with one terminal of the signal 96 whose `other terminal is connected by conductor 123 with the tip or ground spring of jack 44, the contact 50 of this jack being connected with the ground spring 47 of the jack 42, and the contactlO associated with this spring being connected through resistance 124 with the binding post 36, this post having also direct connection with the contact 50 of jack 41. Contact 18 for switch arm 11 is connected by conductor 125 with the contacts 30 and 32 for switch arms 14 'and 15, respectively. Contact 19 for switch arm 11 is connected by conductor 126 with 'the signal lamp 97 whose otherterminal is connected by conductor 121 with the battery spring or jack 44. Contact 20 for switch arm 11 is con- 127 with signal lamp 98 whose other terminal is connected by conductor 123 with the ground spring 47 of jack 44. The contacts 21, 22,24 and 25 of switch arm' 12 are connected respectively with the contacts 16, 17, 19 and 20 of the switch arm 11.

Contact 28 for switch arm 13 is connected by conductor 128 with the conductor 123 `which connects signal 96 with the ground for switch arm 13 connects with conductor -128 through a resistance 129, and contact 27 is connected byconductor 130 with the contact 34 of the switch arm `15. The contact 33 for switch arm 15V is connected by conductor 131 with the contact 23 for switch arm 12. The contact`29 of switch ductor 132 with jack 43 and contact 31 .is connected by condurtor 133 with the ground spring 47 of this Jac r. y

The signal'lamp 99 isconnected `with the arm 14 is connected'by conplugs of the answering.

the battery spring 48A of'i the switch'farm binding post 35 and with the conductor 121 leading to the battery spring of jack 44. The springs 92 and 93 of key 90 connect rcspectively with conductors 108. and 116 which lead to switch arms 14 and 15. Normally the circuit bridged across these switch arms includes the resistances 58 and 70 and the ammeter upon depression keys 86 to 89, but, when the key 90 is depressed, the switch arms 14 and 15 will be directly connected together and the resistance and ammcter short-circuited.

To supply ground and battery connection to the test set, I have shown subscribers are swering cords'A plugged into spring jacks 43 and 44, the cord in jack 43 supplying battery and ground for the contacts 29 and 31,

respectively, for switch arm 14 and there` directly with binding posts 38, 39 and 40, or

a cord circuit connected with the jacks 45 and 46, the various switch levers can be operated to set up circuits to include the relays to be tested, and signal circuits for the relay contacts. After setting up desired resistances, the keys 86 to 89 are depressed to subject the relay winding to various current flows whose values are indicated on the ammeter.

The connections required and the various adjustments necessary to carry out a number of tests will now be described. On F ig. 4 a connecting cord 135 is plugged into spring jack 45 and into the jack 136 of a central station switch-board.' In the switchboard circuit, the cut-oit relay 137 connects with ground and with the tip contact of the switchboard jack. The conductor 138 which extends fromthe ring spring of the jack to ground through battery includes the contacts 139 of the cut-oli relay and the winding 140 of the line relay. The conductor 141 which extends to ground from the sleeve spring of the jack includes the contacts 142 of the cut-ott' rela-y and the winding 143 of the line relay. The line lamp 144 connects with battery, and through contacts 145 with ground in the ordinary manner. Normally the contacts 145 are open and contacts 139 and 142 are closed.

Suppose it is desired to test the line winding 143v for operation, non-operation, non-release and release. The relay winding being connected with the line and consequently with switch arm 13,

relay and switchxarm 15 is moved to contact 34 to connect the circuit with the resistance andl ammeter, and in order to supply battery for the circuit, the switch arm 14 is connected sleeve side of the` 1s moved to its contact 27.

45, the sleeve side of cord 135 and sleeveA spring of the switchboard jack 136, conductor 141, contacts 142, and the relay windmade for the other testing) ing 143 to Ground. The'resistance brushes are primarily all to the right to include thev full resistance, and setting for desired test current flows is made. The key 86 is first closed and brushes 63and 71 adjusted along the respective resistances until the anuneter shows the desired testing operating current, say .0115 amperes. Key 87 is then closed and brushes 64 and 72 adjusted until the ammeter indicates the-desired non-operating current flow, say .009 amperes. Key 88 is .then closed and brushes 65 and 73 adjusted for non-releasing or holding current, say .006 amperes. If the relay 1s to be Itested for releasing current, the locking key 89 Should be depressed until locked. The reason for this is that in telephone systems there is usually a leakage iiow through the various lines and cables, this current iow being always present, and when a test is made the tested relay should a'lways be subj ected to this current fiow. Therefore, when this leakage current is taken into account, the releasin key 89 is locked and adjustment made y brushes 66 and 74 to set the ammeter for the proper releasing current flow, say .004 amperes, before adjustment is current iiows through circuits controlled y the keys 86, 87 and 88. After such setting up, the relay 143 may be tested and the results of the tests will in this case be indicated bythe line lamp 144. To test the relay with operating current the key 86 is depressed and the corresponding test circuit closed. Lighting of the line lamp indicates response of the relay to such operating current. Key 86 is then released and key 87 is then depressed to close the circuit for a owcf' .009 amperes. If the relay is properly adjusted, it will not become sufficiently energized under such current How to close the signal lamp circuit and the lamp will not'light, To test for non-releasing, both keys 86 and 88 are deressed to cause response of the relay and iighting of the lamp 144. The key 86 only is then releasedv so that current flow is reduced to .006 amperes, and'if the relay fails leased to reduce the current iiow to'.004,y

which ,is the releasing current, and the rela releases and the lamp goes out, then it 1s properly adjusted for releasing current, it `being understood that releasing ,currentrepresents the leakage current the relay is subjected to in actual service and that the relay must not operate with such leakage or releasing current therethrough. If the relay fails to properly operate under the various test current flows therethrough, adjustment is usually rnade by adjusting the tension of the relay springs or the position of the arma ture with reference to the core.

If it is desired to test the relay winding 140 connected with the ring side of the line and with battery, the switch arm 14 is moved to the ground Contact 31. to get ground con-` neotion through the cord A connected with jack 43, the circuit being from the battery through winding 140, contacts 139, the ring through conductor 118 to switch arm 12,'

conductor 131, switch arm 15, conductor 116, key 91, ammeter coil 84, conductor 109, resistance 58, test keys 86 to 89, resistance 70, condyctor 108, switch arm 14, contact 31, conductor 133, and through spring jack 43 and cord A to ground. If the same current values are desired' as for the test of relay winding 143, the various keys 86 to 89 are actuated in the same manner as,4 above described, the signal lamp 144 serving to indicate the results of the test. If diHerent current values are desired, then different adjustment must be made of the brushes on the resistances 58 and 70.

In the above tests, the switch-board or line lamp indicates the results of thectests. Where signals are not available yon the switch-board, the test set signals are utilized for indicating whether or not the relay contacts have been properly operated. SuppOs the cut-ofi' relay 137 is to be tested. |This relay being grounded, battery connection must be provided, and switch 14 is connected with battery contact 29.v We then have the following,r circuit: from battery through switch arm 14 to the resistances, ammeter andv keys 86 to 89, to switch arm 15, to contact 32, conductor 125 to contact v18, through switch arm 11 and conductor 117, and through the tip-side of the jack 45, cord 135 and switch-board circuit, and throughrelay 137 to ground.- Resistance adjustment is then made for the desired test current Hows and the keys 86 to 89 are then operated to get the required tests. In order to determine whether the relay properly actuates its lowing signal circuitffrom battery through line relay winding 140, to contacts 139, conductor 138, through cord 135 and jack 45, conductor 118, switch arm 12, to contaciJ 22,

through conductor 122 and through the, sig- 13o" nal 96. The signal will now respond as the various current testing circuits are controlled by the keys 86 to 89 and the results of these tests can be determined. If the relay contacts were connected with ground instead of battery, then the switch 11 would be shitted to contact 16 to utilize the signal 95 which has connection with battery through conductor 121. In the tests just referred to, the'signals 95, 96 are utilized because the signal circuit has the high resistance of the winding 140 therein. For low resistance signal circuits, the lamps 97, 98

will be utilized and connection made of' switch arm 11 with contacts 19 or 20, depending upon whether the tested relay contacts are connected with ground or battery.

By meansof the switches, setting can be made for many other tests of relay and signal circuits without disconnecting any of.-

the relays or circuits from service. Byplugging subscribers cord circuits into the test set jacks 45 and 46, the relays, resistances and contacts connected therewith can be accurately tested. The key 90, as already eX- plained, is bridged across the switch arms 14 and 15 and is used for shortening the resistance and ammeter out of circuit before each test in order to send saturating current flow through the relay to be tested before a test is made, such saturation insuring uniformity and accuracy of the tests. u u

1t will be apparent from the circuit diagram, Fig. 5, that in making all of the above tests in which the adjustable resistance coils and 8() are included, said resistance coils are connected in series and the conductor interconnecting these coils is normally open at the contacts of keys 86, 87, 88, and 89. In

other words, in setting up the apparatus to.

be tested it is connected in series with an ammeter and a source of current and the two adjustable resistance coils 58 and 70. r1`hese resistance coils are each tted with four sliding contacts which may be moved along the surface of the coil for the urpose of obtaining the desired amount o resistance in the test circuit. VEach of the sliding contacts on the coil 58 is connected to one of the sliding contacts of 'the coil 70, the connections between these contacts being normally open at the keys 86 to 89 inclusive. When the contacts on the resistance coils have been properly set for their respective tests, said tests can be rapidlv made by suc- Y cessively depressing each of the keys 86 to 89, thereby connecting a portion .of the `resistance of the coils 58 and 70 in circuit with the source of current, the ammeter, and the apparatus to be tested. -Whenever a test is made by-depressing one ofthe keys 86 to 89 inclusive, such test will be made 'absolutely independent of the otherresistance settings on the coils 58 and 70, as these circuits are- 5, normally open` at the -key contacts. Obviously more than four such test circuits can be set up simultaneously and likewise more than two adjustable resistance coils can be used. lVith this circuit arrangement it is possible to set up a large number of tests for a piece of apparatus and then successively subject said apparatus to these tests without in any way disturbing the resistance settings. This is particularly advantageous when tests are to be duplicated on a large number of pieces of apparatus of like character, for under such circumstances when the resistances have been set, the apparatus can be readily and rapidly tested without any further setting of the test set by the mere operation of the keys 86 to 89 inclusive.

Thatis claimed is: l. In an electrical testing set of the class described, the combination of a plurality of terminalsv with whichrelays or other de ,vices 'to be tested may be connected, a cur- 'rent measuring circuit, switches for selecrality of adjustable resistance coils, a

plurality of branch circuits, and a predetermined resistance in each branch said resistance comprising a part of each one of said.coils, keys for selectively connecting, said branch circuits with said test-ing circuit, a-nd a current measuring instrument connected in said testing circuit.

3. 4In an'electrical testing set of the class described, the combination of a plurality of terminals with which relays or other devices to be tested may be connected, a testing circuit,` switch mechanisms for selectively connecting said testing circuit with said terminals, variable resistance, movable contacts for said resistance for selecting portions of said resistance for inclusion in' the testing circuit, a plurality of keys for selectively closing the testing circuit through the selected resistances, and a current measuringinstrument connected with the testing circuit.

4. In an electrical testing set of the class described, the combination of a current cirsaid current circuit, a Signal circuit, signals connected with said circuit,and switch mechanisms for connecting with said signal circuit the contacts 'cf said electromagnetic switch devlce. l

5. In an electrical testing set of the class described the combination of spring jacks for receiving plugs of cord circuits with which relays are connected, a current circuit, o switches `or selectively connecting the spring jack contacts with said current circuit vto thereby connect the'corresponding cord relay with saidl circuit, resistances, keys for selectively connecting resistances with said current circuit to cause corresponding-current flow therethrough, and a current Ineasuring instrument connected with saidcircuit.`

.6. In an electrical testing set of the class described, the combination of spring jacks -for receiving plugs of cord circuits with which relays are connected, a current circuit, switches for selectively connecting the spring jack contacts with said current circuit to thereby connect the corresponding cord relaywith said circuit, resistances, keys for' selectively connecting resistances with said current circuit to cause corresponding current flow therethrough, a current measuring instrument connected with said circuit, sig.- nal mechanism connected with said circuit, and switch mechanisms for connecting said signal circuit with the contact of the switch jack with which contacts of the tested relay are connected whereby the signals will ree spond in accordance with' current ow through the current circuit and relay.

7. In an electrical testing set, the combination of a supporting hase, terminals ony said base for the connection of devices to be tested, adjustable resistance on said base,'an electrical indicating instrument, testing circuits including portions of said resistance and connected with said terminals, current source terminals n said support connected with said circuits, and keys for said circuits for controlling the successive closure thereof and inclusion in said circuits of the device to be tested connected with said` terminals.

-8. In an electrical test set of the class described, the combination of a supporting base, spring jacks on said base for connection with cords with which devices to be tested are connected, switches on said supporting base comprising switch arms connected with terminals of said spring jacks, contacts for said switch arms and current and signaling circuits leading therefrom, adjust-able resistance, a current indicating instrument on said base, keys on said base for connecting said resistance and instrument in said current circuits, signals on said base included in said signaling circuits, and additional spring jacks for receiving cords with whose conductors battery and ground are connected.

9. In an electrical test set of the class described, the combination of terminals for the connection-of electro-magnetic devices to be tested, a plurality of switch mechanisms each comprising a switch arm and contacts, each terminal being connected with the switch arm of one of said switch mechanisms, signal circuits leading from contacts of said switch mechanisms, target signals in some of-said circuits and lamp signals in the others, ground and battery terminals for said circuits, a current circuit eX- tending from other contacts of said switch mechanisms, an indicating instrument for said circuit, resistances, and switch mechanisms for selectivelyconnecting said resistances in said .current circuit;

10. In an electrical testingset, the combination of terminals for battery and ground and devices to be tested a testing circuit, a plurality of adjustable resistance coils, means for simultaneouslyl settingup a vplurality of resistances with said coilsfor inclusion in said testing circuit, a plurality of keys for selectively and successively con-V necting one of said set-up resistances with said testing circuit, and anelectrical indicating instrument connected with said circult.

11. Inv an electrical test set, a .testing circuit` an adjustable resistance, a second adjustabley resistance, means for simultaneously setting up a plurality of test circuits said circuits each including a'part of said two adjustable resistances, and means thereafter for` successively connecting said set up resistances in circuit with said testing circuit for the purpose of making a plurality of tests. 1

12. In an electrical testing set, a testing circuit, an adjustable resistance consisting of comparatively large units, a second adjustablev resistance consisting of compara- 11@ tively small units, means for simultaneously setting up a plurality of test circuits with said large and. small resistance units, and means thereafter for successively connecting said set up resistances in circuit with said testing circuit for the purpose of making-a plurality of tests.

' 13. A testing circuit comprising in combination, a plurality of adjustable resistances, means interconnecting said resistances, an electrical measuring instrument, a source of current supply and an article to be tested interconnected and connected to said resistances, means for simultaneouslyA setting up a plurality of tests on said re- 125 sistances, and means operable and associated with said interconnecting means for making a plurality of successive tests with said set up resistances.

14. In combination, an adjustable resist- 130 ance comprising comparatively large units, an adjustable resistance comprising 'comparatively small units, circuit' connections including an electrical, measuring instrument, an artlcle to be tested and a source of current supply, means for simultaneously setting up a plurality of resistance combinations on said resistances, and means to successively connect each of said resistance combinations in circuit for the purpose of testing said article.

` 15. A testing circuit comprising in combination, a plurality of adjustable resistances, an electrical measuring instrument, a source of current supply and an article t0 betested serially connected to said resistances, a plurality of conductors normally interrupted interconnecting said resistances, and means operable to successively complete theconnection in each of the conductors interconnecting said resistances whereby said article will be subjected to a plurality of tests.

16. In combination, an adjustable resistance comprising comparatively large units, an adjustable resistance comprising comparatively small units, an electrical measuring instrument, a source of current supply and Copies of this patent may be obtained for ve cents each, by addressing the Y atively small units,`

an article to be tested serially connected to said resistances, a plurality of'conductors normally interrupted "interconnecting said resistances, and means operable to successively connect the conductors interconnecting said-resistances whereby said article will be subjected to a plurality of tests.

17. In combination, an adjustable resistance comprising comparatively large units, an adjustable resistance comprising compara plurality of slidable contacts associated with each of said resistances, an electrical measuring instrument, a sourceof current supply and an 'article to be tested serially connected to saidresistances, a plurality. of conductors normally 'interrupted interconnecting the slidable contacts of said resistances, said slidable contacts being variously set for the purpose of a plurality of tests, and means operable to successively connect the conductors interconnecting the slidable contacts whereby the article to be tested will be subjected to a plurality of tests.

In witness whereof, I hereunto subscribe my name this 22nd day of May, 1916.

BENJAMIN H. SKINNER.

Commissioner of yatents,

Washington, D. c. 

